Primary Lens Luxation

Find out if your dog could develop Primary Lens Luxation (PLL) caused by ADAMTS17 at CAGT.

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Overview

Primary lens luxation (PLL) is a painful and potentially blinding inherited eye disease that typically affects dogs between 3 and 8 years of age and in many breeds is caused by a single nucleotide substitution in the ADAMTS17 gene.

PLL is the term given to the spontaneous displacement or movement of the lens from its normal position within the eye, as a result of rupture of the lens zonules that hold the lens in its normal position. The zonules are a network of tiny fibres that attach the edge of the lens to the ciliary muscle that circles the eye, in the same way that springs attach a trampoline to its frame. Following zonule rupture the lens usually moves to the anterior chamber at the front to the eye where it can cause damage and rapid onset glaucoma by obstructing the drainage of fluid out of the eye resulting in an increase of pressure within the eye. Glaucoma can cause irreversible vision loss if not treated quickly. PLL is invariably bilateral (occurs in both eyes), although a period of several weeks or months might separate luxation of the two lenses. Clinical signs of PLL include sudden onset of eye pain, clouding of the cornea (the front of the eye will look blue), redness of the “white” of the eye and a reluctance to exercise. PLL should be considered an emergency and veterinary assistance sought immediately.

Lens Luxation can also occur secondary to other primary eye disorders, including primary glaucoma, cataracts, inflammation and trauma.

Autosomal Recessive

The single nucleotide substitution in the gene called ADAMTS17 that causes primary lens luxation (PLL) in many breeds is recessive.  This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop PLL during their lives.  Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop PLL as a result of the ADAMTS17 mutation, but they will pass the mutation onto about half of any offspring they have.  Breeding dogs that will not develop PLL should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.

Carriers can be bred from safely, provided they are mated to a dog that has also been tested and is clear of the ADAMTS17 mutation (i.e. carry no copies of the mutation). If a carrier is mated to a clear dog approximately half of the resulting puppies will also be carriers,  so should be tested themselves prior to breeding.  Breeding carriers to tested, clear dogs is safe, in terms of avoiding dogs affected with PLL, and will help to maintain the genetic diversity of a breed. It is therefore encouraged, particularly in the first few generations following the availability of a new genetic test, so that other desirable characteristics and traits can be preserved before the frequency of the disease mutation within the breed is gradually reduced.

Gene ADAMTS17
Variant Single base substitution c.1473+1G>A
Assay Type Variant Specific
Inheritance Autosomal Recessive
Severity Moderate: Affected animals experience significant discomfort or dysfunction, management/treatment costs may be relatively high and life expectancy can be reduced.
Publication

1. Farias FH, Johnson GS, Taylor JF, et al. (2010) An ADAMTS17 splice donor site mutation in dogs with primary lens luxation. Invest Ophthalmol Vis Sci. 51(9): 4716-4721. DOI: 10.1167/iovs.09-5142.

2. Gould D, Pettitt L, McLaughlin B, et al. (2011) ADAMTS17 mutation associated with primary lens luxation is widespread among breeds. Veterinary Ophthalmology. 14: 1-7. DOI: 10.1111/j.1463-5224.2011.00892.x.

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